1. Technical Field
The present disclosure relates to a lithium ion secondary battery.
2. Related Art
Lithium ion secondary batteries are typically required to prevent the short-circuiting between positive and negative electrodes for sure even in the occurrence of the thermal contraction of a separator held between the positive and negative electrodes or the displacement of the separator relative to the electrode. For this reason, the separator is designed to have a larger area than the positive and negative electrodes. On the other hand, another known lithium ion secondary battery includes a separator with high heat resistance (hereinafter referred to as “heat-resistant separator”). For example, JP-A-2009-277397 has disclosed a lithium ion secondary battery in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween. This separator includes at least a microporous film layer mainly formed of thermoplastic resin, and a porous layer mainly including filler with a heat resistance temperature of 150° C. or more. Since the heat-resistant separator does not contract that much under high temperature, the internal shot-circuiting between the positive and negative electrodes can be suppressed. For this reason, it has been known that the lithium ion secondary battery with the heat-resistant separator has relatively high safety.